Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Teachable - Create and sell beautiful online courses with the platform used by the best online entrepreneurs to sell $100m+ to over 4 million students worldwide.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Clever - syncing between education applications for K-12 schools
Slack - A messaging app for teams who see through the Earth!
Claroline - Claroline is a collaborative eLearning and eWorking platform.